Chain hoists, today typically driven by associated electric motor drives, have long been used for the selective, power-driven lifting and lowering of loads comprised of a wide variety of objects and materials. In order to prevent unintended and undesired overloading of such hoists and protect them from structural damage should, for example, the load-engaging hook which is carried by the hoist become caught or entangled or snagged on a heavy or substantially immovable protruding obstacle, it is known to provide the hoist with a slip clutch such, for example, as is disclosed in Federal Republic of Germany Patent No. 3,525,665. It is also known to equip a hoist with a centrifugal brake and detent pawls which, when a rotatable part of the hoist reaches or exceeds a predetermined speed of rotation deemed to be excessive, are driven by centrifugal force in opposition to the urgency of springs into engagement with detent noses or projections so as to effect extremely rapid braking of the hoist. Slip clutches and centrifugal brakes have, however, heretofore been separately utilized with hoists, have been so utilized to only a limited extent--most particularly in conjunction with relatively small hoists--and are expensive to implement.
Because of the possibility of injury to persons, structures or objects on unintended or accidental falling or other unusually rapid descents of hoist-carried loads, the operational dependability of hoists is a matter of great importance. Significantly, the structural and operational safety of hoists is a function not only of the care and design specifications provided by the manufacturer but, in addition, of the quality of user maintenance carried out both preventatively and in response to specific problems that arise in the course of their use. Thus, deficient or improper maintenance of an operative brake or slip clutch in a hoist can result in the required frictional moments being insufficient to accommodate an emergency situation whereby the load can no longer be supported and/or controlled.